Graphene has been the focus of significant interest in both academic and industrial settings. With exceptional electronic, mechanical, and thermal properties, it is widely hailed for a range of applications from high-speed electronics and energy storage devices to electrochemical sensors. More recently, it has been used as a new biocompatible, conductive biomaterial for drug delivery, stem cell differentiation, biosensors, imaging, and osteo, cardiac, and neuro tissue engineering and regeneration. The direct manipulation of graphene, on micro- and macroscopic scales, is desirable for many of these applications. In this regard, digital, additive, and solution-phase printing technologies offer a promising approach. For example, inkjet and gravure printing of graphene have been demonstrated for a range of devices including transistors, supercapacitors, transparent conductors, and interconnects. While significant and having many applications, demonstrations to date remain limited to thin film, paper, or hydrogel composite formats.
Three-dimensional (3D) printing is widely considered a revolutionary manufacturing technology, with significant promise in a broad range of fields including tissue and organ engineering. Direct ink writing is an extrusion-based 3D printing technique involving the deposition of a liquid material ink that rapidly solidifies upon extrusion and allows the fabrication of 3D objects layer-by-layer. Direct ink writing is also compatible with multi-material printing, offering a distinct advantage for integrating multiple functionalities in a 3D printing format. Further development of materials compatible with 3D printing will continue to expand its scope and impact. While carbon-composite inks have been previously developed for 3D printing applications, graphene-based inks offer enhanced functionality and improved electrical, mechanical, and biological properties.